1. Field of the Invention
The present invention relates to an image-forming element comprising a transparent support having an image-forming layer provided thereon, for example, a silver halide photosensitive image-forming layer, particularly to a monosheet-type instant photograph, and also to a base support.
2. Description of the Related Art
Various kinds of image-forming elements comprising a transparent support, having an image-forming layer are known. One kind of image-forming element is a so-called xe2x80x9cmonosheet-type instant photographxe2x80x9d, which is generally used in the form of a film unit having a combination of the following: a photosensitive sheet comprising at least one photosensitive silver halide emulsion layer disposed on a support, a cover sheet having at least an acid polymer layer for the purpose of neutralization disposed on another support, and a pressure-breakable container which is disposed between the photosensitive sheet and the cover sheet and contains an alkaline developing solution.
The surface of the photosensitive sheet on the side not having the photosensitive silver halide emulsion layer and the surface of the cover sheet on the side not having the acid polymer layer, that is, the surfaces of the outermost layers of the film unit are often provided with a coating layer containing a lubricating agent, an ultraviolet light absorber, and others in consideration of unloadability from camera and prevention of ultraviolet-induced deterioration of images. Previously, since this coating layer was formed on a coating layer of gelatin for photographic use provided on a support, acetylcellulose was used as a binder in the coating layer. However, when an acetylcellulose coating layer including a lubricant and an ultraviolet absorbent was formed on a gelatin layer, a layer adhesion problem would occur such that the coating layer would easily peel from the support.
In order to overcome this layer adhesion problem, patent applications have disclosed binder resins for the coating layer containing ultraviolet light absorber to be provided on the gelatin layer. For example, Japanese Patent Application Laid-Open (JP-A) No. 9-297382 discloses the use of acetylcellulose containing a maleic anhydride copolymer and a compound having at least two isocyanate groups; and JP-A No. 10-83049 discloses the use of acetylcellulose containing a maleic monoester copolymer and a compound having at least two isocyanate groups.
The layer-adhesion problem can be solved using the aforementioned specific binders. However, the coating layers of the supports provided with the coating layer disclosed in JP-A No. 9-297382 and JP-A No. 10-83049 use coating liquids with ultraviolet absorbents and binders dissolved in solvents. Therefore the coating layer can be improved with respect to its environmental impact. In addition, since the ultraviolet light absorber incorporated in the coating layer bleeds out to the surface of the layers over time to thereby greatly reduce the transparency of the support, and the image density when seen from the back is greatly lowered. Another imaging performance problem is that after bleeding out the ultraviolet light absorber migrates to the silver halide emulsion layer during the manufacturing process and then, comes into contact with the alkaline developing solution after being removed from a camera, thereby producing a yellow discoloration.
Japanese Patent Application No. 11-269565 filed by the present applicant discloses a monosheet-type instant photograph, designed to prevent both the bleeding out of the ultraviolet light absorber on the outermost layer side of the film unit and the bleeding-induced image density reduction, by using of an ultraviolet light absorber having a carboxyl or sulfo group in the molecule and a specific chemical structure and by forming as a coating layer an acetylcellulose layer containing a compound having at least two isocyanate groups. However, even this monosheet-type instant photograph cannot completely prevent bleeding out. Moreover, the coating layer is formed by coating the coating layer components with an organic-solvent, thus the environmental problems remain.
In response to the adverse environmental effects caused by coating the support with the solution containing a solvent, the present inventors attempted to incorporate the ultraviolet light absorber in a water-based coating liquid to form the coating layer. However, it was impossible to incorporate the ultraviolet light absorber in an amount necessary to exhibit a sufficient ultraviolet absorbency into a thin layer of the coating layer and, in addition, the bleeding out problem was not improved.
As stated above, the manufacture of a high-performance monosheet-type instant photograph, free of the ultraviolet light absorber bleeding out, by a method having little adverse effect on the environment has not yet been established.
In view of the above, it is an object of the present invention to provide an image-forming element and a base support free of a bleeding out of an ultraviolet light absorber by kneading an ultraviolet light absorber into the support of the image-forming element having an image-forming layer on one of the sides of the support.
The object of the present invention can be achieved by providing the following image-forming elements.
According to the first aspect, the present invention is a base support at least having a transparent polyester film containing an ultraviolet light absorber incorporated thereinto by kneading, wherein the ultraviolet light absorber is at least one kind of ultraviolet absorbers characterized by exhibiting a loss of mass of not greater than 10% when heated to 300xc2x0 C. at a heating rate of 10xc2x0 C./minute under a nitrogen gas atmosphere.
According to the second aspect, the present invention is a base support at least having a transparent polyester film containing an ultraviolet light absorber incorporated thereinto by kneading, wherein the ultraviolet light absorber is at least one kind of ultraviolet absorbers characterized in that the difference between the b-value of the sheet having a thickness of 1.5 mm formed after heating a polyester resin, which contains an amount of 0.4% by mass of the ultraviolet light absorber and has a water content of 50 ppm, for 1 minute at 300xc2x0 C. and the b-value of the sheet having a thickness of 1.5 mm formed after heating the same resin for 8 minutes is not greater than 3.0.
According to the third aspect, the present invention is a base support at least having a transparent polyester film containing an ultraviolet light absorber incorporated thereinto by kneading, wherein the ultraviolet light absorber is at least one kind of ultraviolet absorbers characterized by exhibiting a loss of mass of not greater than 10% when heated to 300xc2x0 C. at a heating rate of 10xc2x0 C./minute under a nitrogen gas atmosphere and characterized in that the difference between the b-value of the sheet having a thickness of 1.5 mm formed after heating a polyester resin, which contains an amount of 0.4% by mass of the ultraviolet light absorber and has a water content of 50 ppm, for 1 minute at 300xc2x0 C. and the b-value of the sheet having a thickness of 1.5 mm formed after heating the same resin for 8 minutes is not greater than 3.0.
According to another aspect, the present invention is a base support at least having a transparent polyester film containing an ultraviolet light absorber incorporated thereinto by kneading, wherein the ultraviolet light absorber is at least one kind of ultraviolet absorbers represented by the following general formula (1): 
wherein X1, Y1, and Z1 each independently represents an alkyl group, an aryl group, an alkoxy group, an aryloxy group, an alkylthio group, an arylthio group, or a heterocyclic group, which groups may each be substituted or unsubstituted, with the proviso that at least one of X1, Y1, and Z1 represents a substituent represented by the following structural formula (A): 
wherein R1 and R2 each independently represents a hydrogen atom, a halogen atom, an alkyl group, an alkenyl group, an aryl group, an alkoxy group, an aryloxy group, an acyloxy group, an alkylthio group, an arylthio group, an amino group, an acyl group, an oxycarbonyl group, a carbamoyl group, a sulfamoyl group, a carboxyl group or a salt thereof, or a sulfo group or a salt thereof, which groups may each be substituted or unsubstituted, with the proviso that adjacent R1 and R2 may join together to form a ring.
According to still other aspect, the present invention is an image-forming element comprising a base support and an image-forming layer on one of the sides of the support, wherein the base support is the base support described above.